• Joint appointment to Department of Horticulture & Crop Science (http://hcs-dev.cfaes.ohio-state.edu/)
• Courtesy appointment to Department of Plant Pathology (http://plantpath.osu.edu/)
• Member of Center for Applied Plant Sciences (https://caps.osu.edu/)
• Member of Cellular, Molecular and Biochemical Sciences Program (https://cmbp.osu.edu/)

Summary of Research in the Mackey lab

Induced immune responses are critical to maintaining plant health despite constant assault by potential pathogens. The responses must be strongly and swiftly activated in order to be effective. However, the same responses are detrimental to growth and reproduction if inappropriately activated. Thus plants use exquisite molecular control mechanisms to ensure timely activation of specific defenses in response to proper stimuli and also to limit the magnitude of those responses. Conversely, potential pathogens deploy virulence factors, including effector proteins and toxins, that target and disrupt plant immune responses. In the Mackey lab, we seek to understand fundamental properties of the plant immune system and its targeting by pathogen-derived virulence factors.

MAJOR PROJECTS

1. Role of RIN4 in plant immune responses

Our lab has demonstrated that RIN4, an Arabidopsis protein conserved across plant lineages, plays a key role in regulating two distinct branches of the plant immune system. RIN4 negatively regulates responses elicited by microbe associated molecular patterns (MAMPs), often referred to as MAMP-triggered immunity. Its function as a regulator of this first branch of the immune system has made RIN4 a ripe target for the defense suppressing activity of pathogen-derived virulence effectors. A second branch of the plant immune system, often referred to as effector-triggered immunity or gene-for-gene resistance, is activated when disease resistance (R) proteins perceive the presence of pathogen effectors. Multiple R-proteins interact with RIN4 and respond to its perturbation by effectors.

Ongoing studies investigate the role of RIN4 in regulating plant immunity. How interaction with other proteins and modifications of RIN4, including phosphorylation and proteolysis, affect its structure, sub-cellular localization, and function are areas of active investigation. The work is providing fundamental advances in our understanding of how plants balance the two branches of their immune system to produce robust, yet appropriately expressed responses.

2. Targeting of host cells by a conserved family of bacterial effector proteins

Our lab has advanced two fronts in understanding of the function of AvrE-family of type III effectors, which are widely conserved among and contribute to the virulence of numerous genera of plant pathogenic bacteria. First, we have identified the regulatory subunit of heterotrimeric protein phosphatase 2A as a direct target of two AvrE-family effectors, one from Pseudomonas syringae that is a pathogen of tomato and Arabidopsis and another from Pantoea stewartii that is a pathogen of maize. Ongoing studies seek to understand the molecular basis of this interaction and the molecular and physiological consequence to cells of the host plant.

We have also demonstrated that a bacterial pathogen, Pantoea stewartii, elicits expression of numerous genes controlling maize metabolism and alters the levels of numerous metabolites in susceptible maize leaves. These changes, which require the action of its AvrE-family effector and correlate with the ability of that effector to promote the virulence of the bacteria, alter not only the abundance of various metabolites, but also their abundance in the apoplast, which is an extracellular space where the bacteria can reside and proliferate. Ongoing studies include a system level investigation of the relationship of transcriptomic and metabolomic changes, targeted investigation of the biological functions of select metabolites and the genes encoding enzymes putatively involved in their biosynthesis, and investigation of how accumulation of metabolites in the apoplast affect bacterial viability and nutrition and plant defense signaling.

3. Structure of the plant defense network supporting cell wall fortification

During plant immune responses, a complex signaling network converges on common responses, including cell wall fortification. Despite attack by pathogen-derived virulence effectors, sector compensation maintains robust function of the network. Thus, it is hypothesized that host-adapted pathogens deploy effectors that collaborate to suppress immunity by targeting multiple sectors of the network.

Our lab has shown that cell wall reinforcement in Arabidopsis thaliana following challenge with Pseudomonas syringae is targeted by three key bacterial virulence factors, two effector proteins (including an AvrE-family member) and the coronatine toxin. The data indicate that these effectors distinctly target multiple signaling pathways that contribute to the cell wall defense, including hormone signaling and secondary metabolite production. Ongoing studies seek to understand how these effectors collaboratively disrupt the overall signaling network by targeting discrete signaling sectors.

NOTABLE JOURNAL ARTICLES

• Eschen-Lippold, L., X. Jiang, J.M. Elmore, D. Mackey, L. Shan, G. Coaker, D. Scheel, J. Lee 2016. Bacterial AvrRpt2-like cysteine proteases block activation of the Arabidopsis mitogen activated protein kinases, MPK4 and MPK11. Plant Physiol. DOI:10.1104/pp.16.00336.
• Jin, L., J.H. Ham, R. Hage, J. Soto-Hernández, S.Y. Lee, S.M. Paek, D. Majerczak, M.G. Kim, C. Boone, D.L. Coplin, and D. Mackey 2016. Direct and Indirect Targeting of PP2A by Conserved Bacterial Type-III Effector Proteins. PLoS Pathogens. DOI:10.1371/journal.ppat.1005609: 1-33.
• Asselin, J.E., J. Lin, A.L. Perez-Quintero, I. Gentzel, D. Majerczak, S.O. Opiyo, W. Zhao, S.M. Paek, M.G. Kim, D.L. Coplin, J.J. Blakeslee and D. Mackey 2015. Perturbation of maize phenylpropanoid metabolism by an AvrE-family type III Effector from Pantoea stewartii. Plant Physiol. 167: 1117-1135. 
• Andersson, M.X., A.K. Nilsson, O.N. Johansson, L.E. Adolfsson, F. Pinosa, C.G. Petit, H. Aronsson, D. Mackey, M. Tör, M. Hamberg and M. Ellerström 2015. The isothiocyanate sulforaphane is a signaling molecule of Arabidopsis local defense responses and the hypersensitive response. Plant Physiol. 167: 251-261.
• Breitenbach, H.K., M. Wenig, F. Wittek, L. Jordá, A.M. Maldonado-Alconada, H. Sarioglu, T. Colby, C. Knappe, E. Pabst, D. Mackey, J.E. Parker, and A.C. Vlot 2014. Contrasting roles of apoplastic aspartyl protease AED1 and legume lectin-like protein LLP1 in Arabidopsis systemic acquired resistance. Plant Physiol. 165: 791-809.
• Gangadharan, A., M.V. Sreerekha, J. Whitehill, J.H. Ham, and D. Mackey 2013. The Pseudomonas syringae pv. tomato DC3000 type III effector HopM1 suppresses a non-canonical pathway that promotes PR-1 expression in Arabidopsis thaliana. PLoS One 8: e82032.
• Venkatakrishnan, S., D. Mackey, and I. Meier 2013. Functional investigation of plant specific long coiled-coil proteins, PAMP INDUCED COILED-COIL (PICC) and PICC-LIKE (PICL) in Arabidopsis thaliana. PLoS One 8: e57283. 
• Geng, X., J. Cheng, A. Gangadharan, and D. Mackey 2012. The coronatine toxin of Pseudomonas syringae is a multifunctional suppressor of Arabidopsis defense. Plant Cell 24:4763-74.
• Afzal, A.J., L. da Cunha, and D. Mackey 2011. Separable Fragments and Membrane Tethering of Arabidopsis RIN4 Regulate Its Suppression of PAMP-Triggered Immunity. Plant Cell 10:3798-811.
• Chung, E.H., L. da Cunha, A.J. Wu, Z. Gao, K. Cherkis, A.J. Afzal, D. Mackey, J.L.  Dangl 2011. Specific threonine phosphorylation of a host target by two unrelated type III effectors activates a host innate immune receptor in plants. Cell Host & Microbe 9: 125-36.
• Ham, J.H., D.R. Majerczak, K. Nomura, C. Mecey, F. Uribe, S. Y. He, D. Mackey, and D.L. Coplin 2009. Multiple virulence activities of the AvrE-family proteins WtsE and AvrE1 require G-protein-mimicking motifs. Mol Plant-Microbe Interact 22: 703–712.
• Kim M.G., X. Geng, S.Y. Lee, and D. Mackey 2009. The Pseudomonas syringae Type III Effector AvrRpm1 Induces Significant Defenses by Activating the Arabidopsis NB-LRR-protein RPS2. Plant J 57: 645–653.
• Ham, J.H., M.G. Kim, S.Y. Lee, and D. Mackey 2007. Layered basal defenses underlie nonhost resistance of Arabidopsis toPseudomonas syringae pv. phaseolicola. Plant J 51: 604-616.
• Kim, M.G., L. da Cunha, A.J. McFall, Y. Belkhadir, S. DebRoy, J.L. Dangl, and D. Mackey 2005. Two Pseudomonas syringaetype III effectors inhibit RIN4-regulated basal defense in Arabidopsis. Cell 121: 749-759.
• Belkhadir, Y., Z. Nimchuk, D.A. Hubert, D. Mackey, and J.L. Dangl 2004. Arabidopsis RIN4 Negatively Regulates Disease Resistance Mediated by RPS2 and RPM1 Downstream or Independent of the NDR1 Signal Modulator and Is Not Required for the Virulence Functions of Bacterial Type III Effectors AvrRpt2 or AvrRpm1. Plant Cell 16: 2822-2835.
• Mackey, D., Y. Belkhadir, J.M. Alonso, J.R. Ecker, and J.L. Dangl 2003. Arabidopsis RIN4 Is a Target of the Type III Virulence Effector AvrRpt2 and Modulates RPS2-Mediated Resistance. Cell 112: 379-389.
• Mackey, D., B.F. Holt, A. Wiig, and J.L. Dangl 2002. RIN4 Interacts with Pseudomonas syringae Type III Effector Molecules and Is Required for RPM1-Mediated Resistance in Arabidopsis. Cell 108: 743-754.

For a full list of publications, click here.

EDITORIAL ACTIVITIES

2011 – present Editorial Board, Frontiers in Plant-Microbe Interactions

2011 – present Editorial Board, BMC Plant Biology

2009 – present Associate Editor, PLoS Pathogens

2009 – 2014 Associate Editor, Molecular-Plant Microbe Interactions

2008 – 2014 Editorial Board, Molecular Plant Pathology

Invited Presentations and Instruction

• Manipulation of plant signaling by bacterial effector proteins. Instructior, Illeme Cycle Romand en Sciences Biologiques, September 2003, Villars-sur-Ollon, Switzerland.

• Plant resistance to bacterial pathogens relies on layered basal defense responses. The Sainsbury Laboratory, October 2005, Norwich, United Kingdom.
• Layers of defense restrict the growth of a nonhost bacteria in Arabidopsis. 12th International Congress on Molecular Plant-Microbe Interactions, December 2005, Cancun, Mexico.
• Nonhost resistance to a plant pathogenic bacteria is based on layered defense responses. The American Society for Microbiology General Meeting, May 2006, Orlando, Florida.
• RIN4 is a regulator of immune defense in Arabidopsis and a target of AvrRpm1 from Pseudomonas syringae. The American Phytopathological Society General Meeting, August 2006, Quebec City, Canada.
• Hostilities between Arabidopsis thaliana and Pseudomonas syringae. University of Missouri, September, 2006, Columbia, Missouri.
• Plant innate immunity; how do so few receptors do so much? University of Fribourg, January 2007, Fribourg, Switzerland.
• Confrontation between Arabidopsis thaliana and Pseudomonas syringae: many battles decide the war! Max Planck Institute for Plant Research, January 2007, Cologne, Germany.
• Confrontation between plants and phytopathogenic bacteria: many battles decide the war! Montana State University, April 2007, Bozeman, Montana.
• Basal defenses underlying bacterial resistance. British Society of Plant Pathology Presidential Meeting entitled: Attack and Defence in Plant Disease, September 2007, University of Bath, United Kingdom.
• Dissecting functions of RIN4, an Arabidopsis protein linking basal and R-gene mediated defenses. University of Toronto, April 2008, Toronto, Canada.
• RIN4 is a multifunctional regulator of Arabidopsis immune defense against Pseudomonas syringae. 14th International Congress on Molecular Plant-Microbe Interactions, July 2009, Quebec City, Canada.
• Mechanisms of plant immune function against potentially pathogenic bacteria. Instructor, PhD student workshop on “The interactions between plants and microorganisms: from virulence to symbiosis” Gothenburg University, September 2009, Gothenburg, Sweden.
• Repression versus derepression: regulating the magnitude of plant defense responses against phytopathogenic bacteria. Virginia Tech University, November 2009, Blacksburg, Virginia.
• Repression versus derepression: regulating the magnitude of plant defense responses against phytopathogenic bacteria. Texas A&M University, March 2010, College Station, Texas.
• Practical Summer Workshop in Functional Genomics. Instructor, Ohio State University, June 2010, Columbus, Ohio.
• The virulence activity of WtsE, a key type III effector protein from the maize pathogen Pantoea stewartii. NIFA Awardee Meeting, July 2011, Washington, D.C.
• Practical Summer Workshop in Functional Genomics. Instructor, Ohio State University, June 2012, Columbus, Ohio.
• Complex interplay between pathogens and the innate immune system of plants. Gyeongsang National University, October 2012, Gyeongsang, South Korea.

• Complex interplay between pathogens and the innate immune system of plants. Korean Rural Development Administration, October 2012, Suwon, South Korea.

• Complex interplay between pathogens and the innate immune system of plants. Dong-A University, October 2012, Busan, South Korea.

• Targeting of the innate immune system of plants by bacterial virulence factors. Symposium of the Systems and Synthetic Agrobiotech Center, Gyeongsang National University, October 2013, Gyeongsang, South Korea.
• Direct and indirect targeting of sub-component-specific phosphatase complexes by redundant bacterial type III effector proteins. University of Missouri, October, 2013, Columbia, Missouri. 
• Practical Summer Workshop in Functional Genomics. Instructor, Ohio State University, June 2014, Columbus, Ohio.
• Targeting of specific isoforms of PP2A by a conserved family of type III effector proteins. 16th International Congress on Molecular Plant-Microbe Interactions, July, 2014, Rhodes, Greece. 
• A conserved family of bacterial virulence factors target specific isoforms of protein phosphatase 2A to perturb plant metabolism and defense. The 3rd International Gyeongsang National University Symposium, September, 2014, Jinju, South Korea.
• Studies of model and crop plants reveal molecular and system level functions of a conserved family of bacterial virulence proteins. Purdue University, December 2015, West Lafayette, Indiana.

Former and Current Doctoral Advisees

• Dr. Min Gab Kim - joined lab in 2003, examined the role of Arabidopsis RIN4 and bacterial virulence factors that target it in plant immunity, completed Ph.D. in 2006. Current position - associate professor at Gyeongsang National University, Korea..
• Dr. Luis da Cunha - joined lab in 2003, conducted structure-function analysis of Arabidopsis RIN4, completed Ph.D. in 2009. Current position - associate professor at Federal University of Viçosa, Brazil.
• Dr. Xueqing Geng - joined lab in 2006, analyzed of the function of the bacterial phytotoxin coronatine in Arabidopsis, completed Ph.D. in 2011. Current position – assistant professor at Fudan University, China.
• Anju Gangadharan - joined lab in 2007, characterizing the defense response of Arabidopsis against a non-host-adapted bacterial pathogen. Completed Ph.D. in 2013. Current position - research scientist at Hackensack University Medical Center, USA.
• Lin Jin - joined lab in 2011, describing the targeting of maize and Arabidopsis protein phosphatases by a highly conserved bacterial virulence protein. Completed Ph.D. in 2016. Current position – TBD
• Irene Gentzel - joined lab in 2014, describing the perturbation of maize metabolism by a highly conserved bacterial virulence protein. Ph.D. expected in 2019.
• Alex Turo - joined lab in 2015, describing targeting of maize and Arabidopsis defense signaling network by a consortium of family of bacterial virulence proteins. Ph.D. expected in 2020.